1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The invention also relates to arc chutes for electrical switching apparatus. The invention further relates to arc members for circuit breaker arc chutes.
2. Background Information
Circuit breakers and other electrical switching apparatus (e.g., without limitation, circuit switching devices and other circuit interrupters such as contactors, motor starters, motor controllers and other load controllers) typically include a set of stationary electrical contacts and a set of movable electrical contacts. The stationary and movable contacts are in physical contact with one another when it is desired that the circuit breaker provide electrical current therethrough to a load. When it is desired to interrupt the circuit, however, the movable contacts are moved away from the stationary contacts, thus removing the movable contacts from physical contact with the stationary contacts and creating a space therebetween.
When conducting current, the movement of the movable contacts away from the stationary contacts can result in the formation of an electrical arc in the space between the contacts beginning at the time the contacts are initially separated. Such an arc is undesirable for a number of reasons. For one, it provides a pathway for current to flow through the circuit breaker to the load when it is desired to isolate the load from such current. Additionally, the electrical arc extending between the contacts often results in vaporization or sublimation of the contact material itself, eventually resulting in destruction or pitting of the movable and/or stationary contacts. Thus, it is desirable to eliminate any such arcs as soon as possible.
As shown in FIGS. 1A and 1B, for example, the movable contact 1 is typically mounted on an arm 3 that is contained in a pivoting assembly 5, which pivots the movable contact 1 away from the stationary contact 7. An arc chute 9 is provided along the path of the arm 3 to break up and dissipate such arcs (not shown). The arc chute 9 includes a plurality of spaced apart arc members 11,13 (both shown in FIG. 1A). As the movable contact 1 is moved away from the stationary contact 7, the movable contact 1 moves through at least some of the arc members 11,13 (both shown in FIG. 1A). The arc (not shown) is magnetically urged toward and between the arc members 11,13 (both shown in FIG. 1A). When the arc (not shown) is created, it is more likely to travel along a sharp edge or corner. Accordingly, many arc chute designs employ devices such as, for example, the arc member 11, which in the example of FIGS. 1A and 1B is specifically designed to draw the arc (not shown) into the arc chute 9.
However, at relatively low current levels (e.g., without limitation, about 750 amps), for example, which are associated with an overload condition, there is often insufficient energy to make the arc (not shown) jump to the arc chute 9. For instance, the arc is sometimes attracted to an edge 15 of the stationary contact 7 instead of the arc member 11. It would, therefore, seem logical to position the arc member 11 in as close proximity to the stationary contact 7 as possible, in order to overcome the foregoing disadvantage by facilitating drawing the arc (not shown) to the arc member 11 and, in turn, into the arc chute 9. However, as shown in FIG. 1B, the distance 17 between the arc member 11 and the stationary contact 7 must be at least 0.120 inches. Otherwise, the arc (not shown) would undesirably jump to the arc chute 9 when relatively high current levels (e.g., without limitation, about 22,000 amps), for example, which are associate with a short circuit condition, are experienced. Under such circumstances, a portion of the arc member 11 could vaporize, resulting in a failure to interrupt and/or complete destruction of the arc chamber 19. There is a need, therefore, for an arc member that provides proper circuit interruption under both relatively low current level (e.g., without limitation, about 750 amps) overload conditions and relatively high current level (e.g., without limitation, about 22,000 amps) short circuit conditions.
There is, therefore, room for improvement in electrical switching apparatus, and in arc chutes and arc members therefor.